1. Field of the Invention
The present invention relates to disk drives, in particular, to a servo writer and servo write method for recording servo information (servo pattern) on a disk medium.
2. Description of the Related Art
In general, a disk drive, represented by a magnetic disk drive, has a constitution in which a disc-shaped disk is used as a recording medium, and data is recorded on the disk by a head (magnetic head), or reproduced from the disk.
To record/reproduce data, the head needs to be moved to and positioned in a target position (track position to read/write the data). In the disk drive, a servo system (CPU is a main device) for executing a head positioning control is incorporated. In the servo system, servo information (servo pattern) recorded beforehand on the disk is used to execute the head positioning control.
In the disk drive, the servo patterns are recorded as magnetic servo signals in areas (servo areas) disposed at predetermined intervals (sectors) on the disk.
A manufacturing process of the disk drive includes a servo write process of recording the servo patterns on the disk. For a servo write method, in general, an exclusive-use servo writer apparatus (hereinafter referred to also as a servo track writer (STW)) is used.
In general, the STW includes: an external positioning mechanism, referred to as a positioner, for operating the head incorporated in the disk drive to position the head in the target position on the disk; a clock head; and a servo pattern write circuit. The clock head is used for determining a write timing of the servo pattern.
In the servo write process, this STW is used to execute a write operation of the servo pattern in a state in which a top cover of the disk drive is removed. Therefore, the operation of the servo write process is usually performed in a clean room.
After all the servo patterns are recorded on the disk by the servo write process, the disk drive is removed from the STW. Furthermore, the disk drive is subjected to an attaching process of the top cover and a circuit board, and shifted to a process of function verification.
In the servo write method using the STW, especially the following problem has become pronounced in recent years.
A first problem is that with enhancement of a recording density of the disk drive, high track densification on the disk has been promoted, and the number of tracks for recording the servo patterns has increased. Therefore, a time required for the write operation of the servo patterns per one unit of the disk drive has increased.
One STW is exclusively used by a disk drive until all the servo patterns are written. Therefore, naturally, with the increase of the write time of the servo patterns, the number of STWs needs to be increased in order to enhance efficiency of the servo write process. Especially, to raise the manufacturing yield of disk drives, the number of STWs needs to be further increased.
Moreover, since the operation of the servo write process is performed in a clean room, as described above, it is also necessary to increase the number of clean rooms with the increase of the number of produced disk drives. In short, an increase of the STWs and clean rooms causes an increase in manufacturing costs of the disk drives.
A second problem relates to write accuracy of the servo patterns.
The STW drives/controls an actuator incorporated in the disk drive by the positioner, and executes the positioning control of the head mounted on the actuator. That is, a servo system of the STW feeds back a relative error between the position of the positioner and the target position on the disk, as a control amount, to the positioning control mechanism. In the positioning control mechanism, the position of the positioner is maintained with respect to the target position at high accuracy in order to obtain an operation amount so that the relative error is reduced.
However, in order to write the servo patterns on the disk with high accuracy, the position of the head incorporated in the disk drive with respect to the disk needs to be observed. The existing STW does not include this function. Even when the position of the positioner is controlled with high accuracy, the error of the relative position between the head and disk cannot necessarily be reduced.
Moreover, in the disk drive, the disk is a rotary member attached to a spindle motor, and constantly causes a position fluctuation. Unless the head position is allowed to accurately follow the position fluctuation, the write accuracy of the servo patterns cannot be enhanced.
To solve the above-described problem, a servo write method has been proposed comprising: writing the servo patterns while the top cover is attached to the disk drive, without using any external positioning mechanism such as the positioner. In short, the method is basically referred to as a self-supporting type servo write method (self servo write method) of recording the servo patterns on the disk in a self-supporting manner by the disk drive itself, or a recording servo write method.
Concretely, the following prior arts have been proposed.
A first prior art (see Jpn. Pat. Appln. KOKAI Publication No. 8-212733) is a method comprising: using the head incorporated in the disk drive; determining a timing of the disk in a rotation direction and the head position in a disk radial direction; and recording the servo patterns on the disk in a self-supporting manner.
This method is superior in cost, because it is not necessary to use any external positioner or clock head. In the method, the servo patterns can be written while constantly observing the relative position between the disk and head in the radial direction. Therefore, a high write accuracy can be obtained.
However, the method is easily influenced by jitters by disk rotation, because the writing timing of a disk rotation direction is determined in a self-supporting manner. Furthermore, with an increase of frequencies of the servo patterns, there is a possibility that the servo patterns cannot be connected to one another in joints of tracks. In short, there is a problem of clocking accuracy.
A second prior art (see Jpn. Pat. Appln. KOKAI Publication No. 2001-143416) is a method comprising: a step of writing a servo burst pattern by the servo writer apparatus connected to the disk drive; and a step of using the burst pattern to self-write a final servo burst pattern by the head of the disk drive. This method is also referred to as a partial pre-write recording servo write method.
This method is a recording method which additionally requires a step of performing a pre-write (preliminary write) operation. However, with the use of the pre-write pattern, there is an advantage that track feed pitches can be calibrated. Therefore, there is a possibility that track intervals can correctly be held based on the servo patterns recorded on the disk.
However, this method is also easily influenced by the jitters by the disk rotation, because the write timing of the disk rotation direction is determined in a self-supporting manner. Furthermore, with the increase of the frequencies of the servo patterns, there is the possibility that the servo patterns cannot be connected to one another in the joints of the tracks. In short, there is a problem of clocking accuracy.
In addition to the above-described prior arts, as a third prior art (see Jpn. Pat. Appln. KOKAI Publication No. 2001-243733), a self-supporting servo write method called a magnetic transfer method has been proposed. This method comprises: transferring a servo reference pattern onto the disk by magnetic printing; and attaching the disk to the disk drive. The method further comprises: performing a head tracking operation and clocking operation based on the magnetic printing while writing the servo patterns over the whole surface of the disk.
This method is not easily influenced by the jitters of the disk rotation, and the clocking accuracy is relatively satisfactory. However, since the process of magnetic printing is required, there is a problem in the manufacturing cost. For the tracking operation (positioning operation) of the head, since original board recording is used in a magnetic printing technique, a high accuracy cannot be obtained. This method includes a step of processing an original board, and this processing accuracy determines the write accuracy of the servo reference pattern by the magnetic printing. In short, it is difficult to apply the method to future servo patterns having a high track density.
As a fourth prior art (see Jpn. Pat. Appln. KOKAI Publication No. 1-208777), a transfer-type self-supporting servo write method has been proposed using the disk in which sector servo patterns are written. Here, this method is referred to as a sector pattern type transfer servo write method.
This method comprises: recording the servo reference pattern on the disk by another apparatus; and attaching the disk to the disk drive. The method further comprises: performing the head tracking operation and clocking operation based on the servo reference pattern while writing the servo pattern in the whole surface of the disk.
In this method, in the same manner as in the magnetic transfer-type method, since the servo reference pattern is used in the clocking operation, the correct timing can be obtained. However, since the sector servo pattern is used, a time for writing the servo reference pattern increases with the improvement of the recording density. Therefore, there is a problem in the manufacturing cost.
As described above, in short, in the prior-art self-supporting servo write method, the manufacturing cost can be reduced, as compared with the method using the exclusive-use STW and clean room. However, the recording method and the partial pre-write recording servo write method have the problem that the clocking accuracy is low. The magnetic transfer type method has the problem that the tracking accuracy of the head is low. Furthermore, in the sector pattern type transfer servo write method, the clocking accuracy and tracking accuracy are satisfactory, but there is the problem that it is difficult to reduce the manufacturing cost.